Answers

No, it would make it worse. The immigrants would still have to come, because it still wouldn't be safe to stay in their home countries. The U.S. would still need immigrants to work on its farms. And since fewer would make it, it would need more of them to try.

No. It would stop wildlife migration and cut across at least one Indian reservation (How would you like to have a wall between your bedroom and bathroom or between your house and garage?). As for the asylum seekers, they would simply fly over or travel by boat.